1. Field of the Invention
The present invention relates to a circuit for the comparative vector measurement of keyed radio signal pulses, in particular DME pulses, which arrive approximately simultaneously in a plurality of receivers and which can exhibit large differences in level, and more particularly to such a circuit where, in each receiver, the pulses are fed to a switching amplifier which has an adjustable amplification which can be adjusted in discrete steps and the reduction of which is effected automatically with the rise in the leading edge of the relevant signal pulse, and where, having passed through the particular switching amplifier of the receivers, the instantaneous amplitudes and instantaneous phases of the measuring signals are measured at a specific measuring time which is common to all of the receivers.
2. Description of the Prior Art
In locating technology, in particular, the problem occurs in measuring signal pulses which arrive approximately simultaneously in a plurality of receivers and which possess considerably fluctuating signal levels in respect of amplitude and phase so that, in particular on the basis of the mutual phase position of the oscillations in the wave form of a pulse which has been transmitted and received at a plurality of receivers, it is possible to accurately determine the location of orgin of the signal pulse.
In the U.S. patent application Ser. No. 629,284, a process has been proposed by means of which, at a suitable instant, the output information can be measured simultaneously at all the receiver outputs in order to retain the instantaneous phase and amplitude conditions, so that on the basis of the behavior of each individual receiver it is possible to draw conclusions about the wave front which has occurred at the antenna multiple assigned to the receivers. The measuring time circuit basically consists of a retriggerable, monostable trigger stage which is started by the switching pulses from the switching amplifier. When the spacings between these pulses become greater than the stop time of the trigger stage, which is the case in the vicinity of the maximum, the trigger stage switches over and the switching jump which thus occurs is emitted as an individual measuring time.
However, the function of the measuring time circuit described above is dependent upon the pulse shape. For example, the specification of a DME (Distance Measurement Equipment) pulse determines only the width and the gradient between the 10% and the 90% point. With input levels which are greater than -70 dBm, however, the edge portion located before the 10% point is also included in the signal processing, since this then exceeds the noise level. Pulse shapes can occur which, in the aforementioned example, do in fact fulfill the specifications but simulate a maximum at the leading edge. A pulse shape of this type occurs, for example, when in the transmitted component of a DME interrogation device, the requisite keying depth is achieved in that first of all a high frequency signal modulated with a rectangular pulse is produced which then attains its final form in the transmitter end stage by modulation with a bell-shaped pulse (anode modulation). If such a DME pulse reaches a receiver which deals with the vector measurement, a pulse is formed which, on its leading and trailing edges, is provided with a flattening thereof. In the process corresponding to the aforementioned application, the transition into the portion of constant level leads to the triggering of the individual measuring time, as then the intervals between the switching pulses become too large. This results in a blockage of all the other switching steps, which in the case of a further rising pulse leads to the overmodulation of the switching amplifier.